A gas discharge lamp circuit employing a transistorized oscillator

ABSTRACT

An oscillator circuit for starting and operating gas-filled tubes having a starting mode which provides a signal of high voltage and very high frequency followed by an operating mode after the tube ionizes whereby the voltage and frequency are considerably reduced, but current through the tube is increased. In the operating mode, the impedance of the secondary is substantially the ohmic resistance of the tube so that overall efficiency is very high.

United States Patent 1 1 3,573,5 [72] Inventors Jerome Zonis [56] References Cited Ontario; 0 UNITED STATES PATENTS 2,923,856 2/1960 Greene m1. 315/138 [21] APPL 835364 2 964 676 12/1960 D t 1 315/98 [22] Filed May 21, 1969 av1ese a. 1 [45] Patented A r 6 1971 3,005,130 10/1961 Schwartz....... 315/206 [73] Assi nee i Electmnim 3,084,283 4/1963 Grunwaldt 315/205 g g 3,371,244 2/1968 Boland 315/219 3,396,307 8/1968 Campbell 315/221 Coutmuatlon of application Ser. No. 624,764, Mar. 21, 1967, now abandoned. OTHER REFERENCES Japanese Utility Model Publication No. 21 137/1962, Published July 15, 1961 Devisers: Takeshi Hirasawa 8: Enomoto. Copy in Library Primary Examiner-Roy Lake Assistant Examiner-C. R. Campbell 54 GAS DISCHARGE LAMP CIRCUIT EMPLOYING & Lyon A TRANSISTORIZED OSCILLATOR 13 Claims 2 Drawmg ABSTRACT: An oscillator circuit for starting and operating [52] 11.8. C1. 315/206, gas-filled tubes having a starting mode which provides a signal 315/200, 315/219, 315/238, 315/239 of high voltage and very high frequency followed by an operat- [51] lnt.Cl H05b 41/232, ing mode after the tube ionizes whereby the voltage and H05b 41/233, H05b 41/29 frequency are considerably reduced, but current through the Field of Search 315/98 tube is increased. In the operating mode, the impedance of the 100, 100 (U), 100 (H), 100 (T), 238, 205, 200: 206, 239,243,219

secondary is substantially the ohmic resistance of the tube so that overall efficiency is very high.

GAS DllSCll-llAlltGE LAMP ClllltClUllT EMIPLGYHNG A 'lllltANSllfiTGMZlED GSCHLILATGR This is a continuation of application Ser. No. 624,764, filed Mar. 21 1967 now abandoned.

The present invention relates generally to lighting circuits and more specifically to an improved circuit which increases the efficiency of gas-filled tubes both in the starting and the operating phases as well as the life expectancy of the tube it self. Such gas-tilled tubes include fluorescent tubes, utlraviolet, rare gas tubes such as neons, and vapor devices such as mercury vapor, sodium vapor and the like. The ensuing description will be directed to the application of the circuit to fluorescent lamps with the understanding that the principle of operation with other gas-filled tubes will be the same.

There have been a great number of circuits proposing various types of ballast devices and oscillator circuits to increase the efficiency of operation of fluorescent lamps. A general approach of most of such devices has been to increase the operating frequency of the signal transmitted to the tube and opinions differ considerably as to the optimum frequency at which operation is the most efficient. It seems to be the consensus of opinion that an operating frequency of about 10,000 cycles per second is the most efficient. Some other proposed circuits use this operating frequency to initiate the ionization of the tube or lamp by inserting reactance elements in the lamp circuit so that a high starting voltage is impressed across the lamp, decreasing the ionization time. None of these proposed systems has reached an acceptable degree of efficiency and it is still common in most installations to use conventional ballast units. With such units, the operating life of the lamp is definitely limited, and the operating life will be shortened even more if the number of starts made with the lamp is high.

The particular advantage of the circuit of the present invention is that it provides a means for operating fluorescent lamps with less power input for the same light output, or conversely, at the same power input, brighter illumination is obtained. Another advantage is that the life of the tube is not effected by the number of times ionization is started. For example, manufacturers rate fluorescent tubes in terms of operating hours and number of starts. On a hot cathode tube rated at 7,500 hour lifetime, the maximum number of starts to be expected is about 2,500. A cold cathode tube may be rated at 15,000 to 30,000 hours with an almost indefinite number of starts, but operates at much lower efficiency than the hot cathode type and is not in general use. With the circuit of the present design in excess of 5,000 starts have been obtained with a hot cathode-type tube without a noticeable decrease in the operating performance of the tube.

The reason circuits heretofore proposed have failed to obtain the efficiency of the present circuit is the failure to properly deal with the complex variable impedance of gasfilled tubes. In the present invention the tube impedance is made a very definite part of the secondary circuit and is considered as an ohmic value. Taking the ohmic value of a' specific tube, the values of the other circuit elements are then determined and a well-matched resonant circuit is provided for maximum efficiency with that specific tube. The same circuit will operate other tubes of different size or power requirements but not as efficiently as for the specific tube for which it was designed. It has been found that manufacturers specifications are sufficiently strict so that tubes having the same manufacturers specifications will have very nearly the same mpsdans t lt is an object therefore of the present invention to provide an improved circuit for the operation of gas-filled tubes.

It is a specific object of the present invention to provide a circuit for gas-filled tubes having improved operating efficiency and performance characteristics.

lt is also an object of the present invention to provide a gasfilled tube circuit having decreased starting time.

It is another advantage of the present invention that open circuit operation or breakage of the fluorescent tube will not result in damage to the circuit nor will shorting of the tube terminals.

It is also an advantage of the present invention that light outputs in excess of rated values for particular fluorescent tubes can be obtained without impairing the working life or efficiency of the tube.

Further objects and advantages of the present invention will become readily apparent upon reading the following detailed description in conjunction with the accompanying drawing in which:

FIG. 1 is a schematic circuit diagram of a preferred embodiment of the circuit of the present invention; and

FIG. 2 is a graph representing performance characteristics of the circuit.

In FIG. 1, a transistor 10 is connected as a typical oscillator in which the emitter 11 is connected to the negative electrode 12 of battery 13 through switch 35. Emitter 11 may be directly connected to electrode 12 through switch 35 or through variable resistor 14 and capacitor 15 if it is desired that there be a means for adjusting the input voltage to the circuit. Zener diode 16 is connected between emitter 11 and collector 1'7 of transistor 10 to guard against excessive peak inverse voltages as when the tube is broken, etc. Collector 17 also connected to terminal 13 of the primary winding of transformer 19. The positive electrode 20 of battery 13 is coupled to tap 21 of transformer 19. A diode 22 may be connected in series with positive electrode 20 to prevent damage to the circuit should the connections to the battery 13 be inadvertently reversed. Capacitor 23 may be connected across the series combination of the battery 13 and diode 22 with the polarity shown in instance where the battery 13 may be located some distances from the oscillator circuit in which case the leads would inject some unwanted inductance into the oscillator circuit. Capacitor 23 is thus selected having a value to compensate for any inductance added by the battery leads.

Battery 13 is connected through a base circuit impedance to the base 24 of transistor 10. The base 24 is connected through capacitor 25 to terminal 26 of the feedback winding of transformer 19. A feedback resistor 27 is connected between tap 21 and base electrode 24 and a bypass capacitor 28 is coupled across resistor 27. The base circuit impedance includes resistor 27 and capacitor 25 and 28. Capacitor 28 is selected having a value such that it will protect the base 24 of transistor 10 from peaks occurring in the oscillator circuit.

The secondary winding 29 of transformer 19 has a capacitor 30 coupled in parallel between terminals 31 and 32 thereof. Another capacitor 33 is connected in series with terminal 31 and fluorescent tube 34 which is in turn connected to terminal 32 of transformer 19.

The operation of the circuit of FIG. ll will be described and reference will be made to the wave forms shown in FIG. 2. When switch 35 in the battery circuit is closed, transistor 10 is caused to oscillate at a frequency which is primarily determined by the impedance of secondary winding 29 and the parallel coupled capacitor 30. Since the fluorescent tube 34 is initially cold, it presents an infinitely high impedance at this time. The value of capacitor 30 and the inductance provided by secondary winding 29 is selected so that the frequency at which oscillator circuit initially operates will be from to 200 kc. Winding 29 and capacitor 30 thus form a parallel resonant circuit with a relatively high peak-to-peak voltage appearing across the terminals 31 and v32 of transformer 19. Capacitor 33 will have a value which is large with respect to that of capacitor 30 and thus the high voltage appearing across terminals 31 and 32 will be impressed across the terminals of fluorescent tube 34 as shown by FIG. 2 at the portion designated 36 of the voltage curve 37. The high frequency at this stage is shown at 30 on frequency curve 39 in FIG. 2. The combination of high voltage and high frequency impressed upon tube 34 will rapidly initiate a glow discharge-type of ionization within the tube. This ionization will cause current to start flowing through tube 34 as shown by the lower portion 40 of current curve 41 in FIG. 2.

As more current flows, as indicated by the upward slope of curve 40 with respect to time, ionization will rapidly increase inside tube 34 and the impedance thereof will drop, with the result that the voltage appearing across the electrodes of tube 34 will also drop as evidenced by the downward slope of portion 36 of the voltage curve 37 in H6. 2. The drop in the effective impedance presented by tube 34 also lowers the resonant frequency for the oscillator circuit as shown by portion 38 of the curve 39 in FIG. 2. As these changes occur capacitor 33 becomes a significant factor in the circuit forming a series resonant circuit with secondary winding 29 and tube 34 characterized by having high current and low voltage impressed across tube 34 as shown by portions 42 and 43 respectively of the curves 4] and 37 shown in FIG. 2. As series resonance occurs through capacitor 33, tube 34 and winding 29, the significance of the relatively small capacitor 30 becomes negligible and the operating frequency drops to the value of 30 to 50 kc. These changes all occur in a time of less than 1 second and the resultant illumination obtained from tube 34 is demonstrated by the curve 44 in FIG. 2. As shown by curve 44, light output increases rapidly at the point of ignition of tube 34 to a level of about 1,400 lumens and after additional heating rises to 1,600 lumens. Starting time for the tube used to obtain these values was about 30 milliseconds although this time as well as the other values will vary somewhat with different tubes and input values.

Thus, the circuit operates in two phases, a starting phase characterized by high frequency and high voltage, followed by an operating phase characterized by having relatively low voltage and high current with an operating frequency less than the starting frequency. After current is flowing through tube 34 sufiicient heating occurs within the tube to heat the filaments thereof without the necessity for separate filament heating. This feature eliminates a respectable amount of power normally lost in merely heating the filaments. The high-frequency, high-voltage starting phase very rapidly initiates a glow discharge in the fluorescent tube and the circuit then automatically reverts to a high-current, low-voltage operating phase which is more efficient. At the same time, the frequency drops to a more efficient operating level but one at which increased illumination is still obtained from lamp 34. The dimming circuit provided by resistor 34 and capacitor 15 drops the input voltage as desired, thereby lowering the light output.

As an example of the increased results obtained with the circuit of the present invention, a standard single-pin fluorescent tube manufactured by Sylvania having a code No. F24Tl2, COOL-WHITE, was first connected in a conventional fixture operating at an input voltage of l volts at 60 cycles. This is a 26 watt tube and it provided a light reading of approximately 1,1000 lumens. The same 26 watt tube was then coupled into the circuit made in accordance with this invention in which the input voltage wasv 36 volts. Operating again at an input power of 26 watts, the tube started at a frequency of approximately 150 kc. and after starting provided a light output of approximately 1,600 lumens. After starting, current input was 710 ma. at 42 kc. This represents a percentage increase in light output of approximately 45 percent. In a similar manner, the power input may be reduced 45 percent to about 14.3 watts and still produce the same 1,100 lumens of light output obtained by the conventional circuit.

With respect to life expectancy of the fluorescent tube 34, it has been found that the life is substantially prolonged. Manufactures of hot cathode-type tubes presently estimate the life of a tube at 7,500 hours with an expected number of starts at about 2,500. It has been found using the circuit of the present invention that in excess of 5,000 starts can be made with a hot cathode-type tube without noticeable deterioration.

Thus it can be seen that the circuit of the present invention provides a unique method of operating fluorescent tubes which obtains greater illumination therefrom for a given input power while at the same time prolonging the operating life thereof. While a particular embodiment of this circuit has been shown and described, it will be obvious to persons skilled in the art that changes and modifications might be made, particularly as to the type oscillator circuit used, without departing from the invention in its broader aspects. It is the aim of the appended claims to cover all such changes and modifications as fall within the true scope and spirit of this invention.

We claim:

1. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having a primary and a secondary winding,-said starting frequency being at least in part determined by the transformer; a load circuit connected across said secondary winding, said load circuit consisting of capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor means is decoupled from the transformer when the gas-filled tube is nonconductive; the secondary winding of said transformer being related to the primary winding so as to develop across the secondary winding as soon as said oscillator is energized a high frequency voltage of sufficient magnitude which automatically initiates a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being substantially altered by said capacitor means when the gas tube is conductive.

2. A system as set forth in claim 1 wherein said capacitance of said capacitor means is of sufficient magnitude to control the current through said tube during said operating mode.

3. A system as set forth in claim 1 wherein said capacitance means is of sufficient magnitude to provide a high operating current through said tube with a low-voltage drop across said tube during said operating mode.

4. A system as set forth in claim 1 wherein said oscillator circuit includes: a transistor having a collector, an emitter and a base, said source of electric potential being connected in proper biasing relationship across said emitter and said base and being connected through said collector and said emitter across said primary winding of said transformer, said transformer including a feedback winding connected between said source of electric potential and said base of said transistor, and a base circuit impedance connected between said feedback winding and said base of said transistor for controlling the voltage and current applied to said base.

5. The system as set forth in claim 4 wherein said base circuit impedance includes a feedback resistor and a bypass capacitor connected in parallel between said base and said source of electric potential, and a capacitor connected between said base and said feedback winding.

6. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit including current control device means adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having primary, secondary and feedback winding means; an output circuit connected across said secondary winding, said output circuit including capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor is decoupled from the transformer when the gasfilled tube is nonconductive; the primary, secondary and feedback winding means of said transformer being related to the current control device means to form an oscillator circuit which develops across the secondary winding means a high starting voltage of sufficient magnitude to initiate a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being a frequency substantially different from said starting frequency due to the coupling to said transformer of said capacitor means when the gas tube is conductive; said operating frequency being selected to provide maximum output efficiency from said tube and being the resonant frequency for the inductance of said secondary winding means, the capacitance of said capacitor means and the ohmic resistance of said tube whereby the impedance of the output circuit at said operating frequency is essentially the ohmic resistance of said tube.

7. The starting and operating system of claim 6 wherein said starting frequency is at least a number of times higher than said operating frequency.

8. A system for starting and operating a gas-filled tube comprising: a transformer having primary and secondary windings and a load circuit consisting of capacitor means and a gasfillcd tube connected in series circuit relationship with said secondary winding, means connected to said transformer for driving said secondary winding in a starting mode having a characteristic starting frequency which automatically ionizes the gas in said tube as soon as said secondary winding is so driven and in an operating mode having a characteristic operating frequency to provide alternating current to said tube, and a source of electric potential connected to said driving means.

9. A system as set forth in claim 8 wherein said transformer forms part of a frequency determining portion of an oscillator formed by said driving means, and said transformer in combination with said driving means provides a high frequency voltage across said secondary winding to start the tube during the starting mode.

10. A system as set forth in claim 9 wherein said capacitor means forms parts of the frequency determining portion of the oscillator and has sufficient capacitance to alter substantially the operating frequency of the oscillator when said gas tube is operating.

11. A system as set forth in claim 8 wherein said capacitor means has sufficient capacitance to control the current through said tube during said operating mode.

12. A system as set forth in claim 8 wherein the elements of said system being designed to provide an operating frequency between 30 and 50 kiloHertz.

113. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit including current control device means adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having primary, secondary and feedback winding means; an output circuit connected across said secondary winding, said output circuit including capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor is decoupled from the transformer when the gasfilled tube is nonconductive; the primary, secondary and feed back winding means of said transformer being related to the current control device means to form an oscillator circuit which develops across the secondary winding means a high starting frequency voltage of sufficient magnitude to initiate a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being a frequency substantially different from said starting frequency due to the coupling to said transformer of said capacitor means when the gas tube is conductive, said operating frequency being determined at least in part by the resonant frequency for the inductance of said secondary winding and the capacitance of said capacitor means operating through at least feedback winding means to alter the starting frequency of the oscillator. 

1. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having a primary and a secondary winding, said starting frequency being at least in part determined by the transformer; a load circuit connected across said secondary winding, said load circuit consisting of capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor means is decoupled from the transformer when the gas-filled tube is nonconductive; the secondary winding of said transformer being related to the primary winding so as to develop across the secondary winding as soon as said oscillator is energized a high frequency voltage of sufficient magnitude which automatically initiates a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being substantially altered by said capacitor means when the gas tube is conductive.
 2. A syStem as set forth in claim 1 wherein said capacitance of said capacitor means is of sufficient magnitude to control the current through said tube during said operating mode.
 3. A system as set forth in claim 1 wherein said capacitance means is of sufficient magnitude to provide a high operating current through said tube with a low-voltage drop across said tube during said operating mode.
 4. A system as set forth in claim 1 wherein said oscillator circuit includes: a transistor having a collector, an emitter and a base, said source of electric potential being connected in proper biasing relationship across said emitter and said base and being connected through said collector and said emitter across said primary winding of said transformer, said transformer including a feedback winding connected between said source of electric potential and said base of said transistor, and a base circuit impedance connected between said feedback winding and said base of said transistor for controlling the voltage and current applied to said base.
 5. The system as set forth in claim 4 wherein said base circuit impedance includes a feedback resistor and a bypass capacitor connected in parallel between said base and said source of electric potential, and a capacitor connected between said base and said feedback winding.
 6. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit including current control device means adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having primary, secondary and feedback winding means; an output circuit connected across said secondary winding, said output circuit including capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor is decoupled from the transformer when the gas-filled tube is nonconductive; the primary, secondary and feedback winding means of said transformer being related to the current control device means to form an oscillator circuit which develops across the secondary winding means a high starting voltage of sufficient magnitude to initiate a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being a frequency substantially different from said starting frequency due to the coupling to said transformer of said capacitor means when the gas tube is conductive; said operating frequency being selected to provide maximum output efficiency from said tube and being the resonant frequency for the inductance of said secondary winding means, the capacitance of said capacitor means and the ohmic resistance of said tube whereby the impedance of the output circuit at said operating frequency is essentially the ohmic resistance of said tube.
 7. The starting and operating system of claim 6 wherein said starting frequency is at least a number of times higher than said operating frequency.
 8. A system for starting and operating a gas-filled tube comprising: a transformer having primary and secondary windings and a load circuit consisting of capacitor means and a gas-filled tube connected in series circuit relationship with said secondary winding, means connected to said transformer for driving said secondary winding in a starting mode having a characteristic starting frequency which automatically ionizes the gas in said tube as soon as said secondary winding is so driven and in an operating mode having a characteristic operating frequency to provide alternating current to said tube, and a source of electric potential connected to said driving means.
 9. A system as set forth in claim 8 wherein said transformer forms part of a frequency determining portion of an oscillator formed by said driving means, and said transformer in combination with said drivinG means provides a high frequency voltage across said secondary winding to start the tube during the starting mode.
 10. A system as set forth in claim 9 wherein said capacitor means forms parts of the frequency determining portion of the oscillator and has sufficient capacitance to alter substantially the operating frequency of the oscillator when said gas tube is operating.
 11. A system as set forth in claim 8 wherein said capacitor means has sufficient capacitance to control the current through said tube during said operating mode.
 12. A system as set forth in claim 8 wherein the elements of said system being designed to provide an operating frequency between 30 and 50 kiloHertz.
 13. A system for starting and operating a gas-filled tube, the system comprising: an oscillator circuit including current control device means adapted for connection to a source of electrical potential, said oscillator circuit having a starting mode characterized by a starting frequency and an operating mode characterized by an operating frequency; a transformer connected into and forming a part of said oscillator circuit, said transformer having primary, secondary and feedback winding means; an output circuit connected across said secondary winding, said output circuit including capacitor means and a gas-filled tube connected in series circuit relationship so the capacitor is decoupled from the transformer when the gas-filled tube is nonconductive; the primary, secondary and feedback winding means of said transformer being related to the current control device means to form an oscillator circuit which develops across the secondary winding means a high starting frequency voltage of sufficient magnitude to initiate a glow discharge type of ionization within said tube during said starting mode; and said operating frequency being a frequency substantially different from said starting frequency due to the coupling to said transformer of said capacitor means when the gas tube is conductive, said operating frequency being determined at least in part by the resonant frequency for the inductance of said secondary winding and the capacitance of said capacitor means operating through at least feedback winding means to alter the starting frequency of the oscillator. 